1. Field of the Invention
The present invention relates generally to methods and apparatus for determining a person's visual characteristics, and more particularly to methods and apparatus for determining the sphere and cylinder components of a subjective refractive correction of the eye using objective wavefront measurement.
2. Description of the Related Art
Phoropters are apparatus used by optometrists to determine a patient's visual characteristics, so that proper eye diagnoses can be made and eyewear can be prescribed. In conventional phoropters, a patient views a target image through the phoropter, in which various test lenses are disposed, while an optometrist moves the test corrective lenses into the patient's field of view. The patient is then asked to verbally compare the quality of the perceived image as afforded by one lens versus another lens presented. The optometrist takes note of either an improvement or a deterioration in the patient's vision through such lenses. Systematically, the test progresses towards the “best” test lens entirely based on the patient's subjective responses. The lens parameters so determined are then used as the basis for a prescription for eyewear.
Unfortunately, as recognized herein, the patient can become fatigued during the process and/or misjudge the vision afforded by the various lenses. This can lead to the selection of a less than optimum prescription. Moreover, some patients, such as a very ill or a very young patient, might not be capable of articulating the quality of vision the various lenses afford the patient.
Objective refraction measurements using an auto-refractor are typically fast, require less operator skill and training, and are easier for a patient. However, because an auto-refractor typically does not measure subjective vision quality, it is not acceptable by the clinician as a replacement of subjective refraction measurements, and often an auto-refractor outcome is used as a starting point for subjective refraction measurement.
Wavefront sensing technology provides high degree of accuracy and is capable of capturing aberrations across the entire pupil in an instant. Many efforts have been made using wavefront data to predict a subjective refraction result. Thibos et. al. in “Accuracy and Precision of objective refraction from wavefront aberrations,” published in the Journal of Vision 2004, vol. 4, pp. 329-351, tested 33 objective methods and found that the precision of these estimates is no better than 0.5 D within the 95% limit. It remains a challenge to be able to predict subjective refraction results using an objective measurement to the accuracy level of 0.25 D-0.35 D that offers clinician comfort and trust that such objective measurements can replace a manual phoropter.
Thus, what is needed are improved methods and apparatus for determining subjectively optimal refractive corrections of an eye based on objective measurements.